--- title: "P20 vs S136 steel: which is better for high volume plastic injection molds?" description: "For NPI teams balancing mold cost, surface finish and service life for new 2026 plastic production projects, this guide delivers practical, actionable selection criteria and processing tradeoffs to avoid overspending or unexpected mold failure during mass production." url: "https://www.ok-tool.com/qa/p20-vs-s136-steel-high-volume-injection-molds.html" language: "en" type: "Q&A" category: "Injection Molding Q&A" datePublished: "2026-10-04" dateModified: "2026-10-04" brand: "OK TOOL" manufacturer: "OK TOOL" answerCount: 7 --- # P20 vs S136 steel: which is better for high volume plastic injection molds? ## Question I’m currently finalizing mold material selection for two new ABS component lines that are scheduled to start trial runs in 6 weeks. The first line is a standard black structural housing with 80,000 projected cycle runs annually, and the second is a clear medical-grade PP enclosure that requires a mirror polish finish and 300,000 projected cycle runs over the next 3 years. My procurement team flagged that S136 would push the initial mold budget 42% higher than P20, but our former supplier had a case where P20 rusted halfway through a 120k run with PP parts that have trace additive content. I’m stuck because I can’t justify the full S136 cost to my project lead if P20 can deliver acceptable performance, but I also can’t risk unplanned mold rework that would delay our Q4 2026 mass production launch. I need clear, actionable criteria to split the two mold projects between P20 and S136 instead of picking a single material for both tools. ## Answers ### Answer 1 — Best Answer First, map your two separate tool requirements directly to the inherent material properties of P20 and S136 to avoid blanket decisions. P20 is a pre-hardened low-alloy mold steel with a typical hardness range of 28-32 HRC, while S136 is a martensitic stainless steel that reaches 48-52 HRC after full quenching. The 42% upfront cost gap your procurement team identified in 2026 pricing is driven by S136’s higher raw material purity, additional heat treatment steps, and corrosion resistance alloy content, not arbitrary markup. For the black ABS structural housing mold that targets 80,000 annual cycles, P20 is fully sufficient as long as you implement two small control measures. ABS with no corrosive flame retardant additives will not accelerate P20 rust formation, and 80k cycles sit well below P20’s standard fatigue life limit of 150,000 runs for non-abrasive, non-corrosive resins. You can skip full S136 specification for this tool to lock in the 42% cost savings, and allocate the leftover budget to secondary polish upgrades if you need a finer surface finish than standard P20 as-milled texture. For the clear medical-grade PP enclosure mold, S136 is non-negotiable here. The trace slip agents and peroxide residues in medical PP will cause P20 surface micro-corrosion after 60,000-80,000 runs, which will leave hazy spots on your clear parts that no in-mold cleaning can fully remove. **You can opt for pre-hardened S136 HRC 32 instead of full quenched S136 to cut 18% of the mold cost** while retaining 90% of the corrosion resistance you need for the 300k cycle target, which balances budget constraints and performance requirements. To avoid common mistakes that many NPI teams make with this material pair, do not apply S136 for low-cycle non-cosmetic molds as a one-size-fits-all upgrade, as the extra cost will never be recovered in your total part cost per unit. **Allocate 2 hours of extra IQC inspection for incoming P20 mold steel blanks to confirm hardness values fall within 28-32 HRC with no soft spots**, which eliminates the risk of unexpected tool wear mid-run. For S136 blanks, verify that the supplier has done stress relief treatment before CNC machining to reduce post-processing deformation risk. After trial run sign-off, implement a simple mold maintenance log that requires a thin layer of anti-rust spray to be applied immediately after every production stop longer than 72 hours for the P20 tool. **This simple step extends P20’s actual service life by more than 40% for non-corrosive resin runs**, closing most of the performance gap with S136 for low to medium volume applications. **status:** accepted **Author:** David Zhang **Date:** 2026-10-04 ### Answer 2 The hardness consistency of as-received P20 and S136 blanks will directly impact your total part cost per unit over the full product lifecycle. For the non-critical black ABS housing, even if P20 only lasts 120k cycles instead of 150k, the extra cost of a single mold repair at 100k cycles is still 60% lower than the upfront premium for S136. For medical grade PP applications, S136’s stain resistance means you will not need to stop production every 200 cycles to wipe down the mold surface to remove residue buildup, which cuts your unplanned downtime rate by more than 70% during mass production. You can also consider P20 with a surface nitriding treatment for mid-tier applications that need slightly better wear resistance without switching to full S136, but note that nitrided P20 still does not match S136’s corrosion resistance for acidic or additive-rich resins. **status:** suggested **Author:** Sophia Wang **Date:** 2026-10-04 ### Answer 3 The two steels have different thermal conductivity values that will change your injection cycle time significantly. P20 has a thermal conductivity of roughly 29 W/mK, while S136 at full hardened state sits around 18 W/mK. For the 80k run ABS housing, using P20 will reduce your cooling time by 12-15% per shot, which adds up to over 100 hours of total saved production time across the full production run. If you force S136 for this non-critical part, you will need to adjust cooling line layout to compensate for slower heat dissipation, otherwise you will face higher part warpage and longer cycle times that eat into your production capacity. For the clear PP parts, the lower thermal conductivity of S136 is not a downside, as it enables more uniform cooling across the full cavity surface, which reduces flow mark and haze defect rates for transparent components. **status:** suggested **Author:** Daniel Yang **Date:** 2026-10-04 ### Answer 4 Your incoming inspection criteria for these two mold steels can be adjusted to match your actual usage requirements to avoid unnecessary quality overchecks that delay trial preparation. For P20 blanks, only test three key parameters: surface decarburization layer depth, hardness uniformity across the full block, and sulfur content below 0.01% to prevent micro-cracking during long cycle runs. For S136 blanks, add a copper sulfate spot test to verify full corrosion resistance performance, to avoid situations where suppliers pass off ordinary 420 stainless steel as premium S136 to cut costs. After the mold is completed, the first 50 sample parts from P20 and S136 molds can be batch tested for surface roughness consistency, and you will find that S136 maintains 98% of its initial polish finish after 1000 cycles, while P20’s surface roughness will degrade by around 12% after the same run count. **status:** suggested **Author:** Jason Zhou **Date:** 2026-10-04 ### Answer 5 The machining time for P20 and S136 mold cavities varies by a noticeable margin that many teams do not account for in their total tooling budget. Pre-hardened P20 cuts much faster on standard CNC mills, with tool life for regular carbide end mills reaching 12-15 hours per set, while machining full hardened S136 reduces end mill life by 50% or more. For the mirror polish you need on the clear PP cavity, S136 can be polished to A2 or A1 grade much more easily without generating micro-scratches, while P20 will need 30% more manual polishing hours to reach the same finish level, and still tends to retain tiny pinhole marks from non-metallic inclusions in the steel structure. If you choose pre-hardened S136 at 32 HRC instead of full quenched S136, your CNC machining time will be almost identical to machining P20, which eliminates most of the hidden machining cost premium for S136. **status:** suggested **Author:** Olivia Chen **Date:** 2026-10-04 ### Answer 6 There are small design adjustments you can make to your part geometry to accommodate each steel’s inherent properties and reduce tooling risk. For the P20 mold for the black ABS housing, you can reduce the minimum draft angle for side walls by 0.5 degrees, since P20’s lower hardness means it has lower friction against the flowing resin during ejection. For S136 molds, avoid sharp internal corners that have a radius smaller than 0.8mm, as full hardened S136 has higher notch sensitivity and is more prone to micro-chipping at sharp edges under repeated high injection pressure. If you have any small raised text or fine texture features on the part surface, S136 can hold these features clearly for 300k+ cycles with no edge blurring, while P20’s edges will start to wear after 120k cycles, requiring you to re-engrave the text twice over the full product lifecycle. **status:** suggested **Author:** Kevin Liu **Date:** 2026-10-04 ### Answer 7 You can split the mold manufacturing timeline to accommodate the different lead times of P20 and S136 to hit your 6-week trial run target. P20 blanks are almost always in stock at local steel suppliers, so you can receive the raw material in 2-3 working days, while standard S136 blanks require 7-10 days of lead time if you need full quenched and stress relieved material. This means you can start rough machining the P20 ABS housing mold 1 week earlier to catch up on any unplanned delays during tooling, while scheduling the S136 clear PP mold to enter the production queue right after raw material arrival. If your project timeline slips by 3 days for any reason, you can also use pre-hardened P20 to produce a temporary spare mold for the black ABS parts, which can be finished in half the time of a S136 spare, to ensure you do not miss your mass production launch window even if you encounter unexpected tool damage during trial runs. **status:** suggested **Author:** Eric Zhao **Date:** 2026-10-04 ## Related Resources - [Injection Molding Q&A](https://www.ok-tool.com/qa/injection-molding/) - [Plastic Injection Molding](https://www.ok-tool.com/capabilities/plastic-injection-molding/) - [Injection Molding Guide](https://www.ok-tool.com/manufacturing/injection-molding/) - [Injection Molding Buying Guides](https://www.ok-tool.com/buying/injection-molding/) - [Products](https://www.ok-tool.com/products/) - [Custom Manufacturing](https://www.ok-tool.com/custom-manufacturing/) - [Manufacturing Knowledge Base](https://www.ok-tool.com/knowledge/) - [Injection Molding](https://www.ok-tool.com/knowledge/injection-molding/) ## Structured Data ```json [ { "@context": "https://schema.org", "@type": "QAPage", "mainEntity": { "@type": "Question", "name": "P20 vs S136 steel: which is better for high volume plastic injection molds?", "text": "I’m currently finalizing mold material selection for two new ABS component lines that are scheduled to start trial runs in 6 weeks. The first line is a standard black structural housing with 80,000 projected cycle runs annually, and the second is a clear medical-grade PP enclosure that requires a mirror polish finish and 300,000 projected cycle runs over the next 3 years. My procurement team flagged that S136 would push the initial mold budget 42% higher than P20, but our former supplier had a case where P20 rusted halfway through a 120k run with PP parts that have trace additive content. I’m stuck because I can’t justify the full S136 cost to my project lead if P20 can deliver acceptable performance, but I also can’t risk unplanned mold rework that would delay our Q4 2026 mass production launch. I need clear, actionable criteria to split the two mold projects between P20 and S136 instead of picking a single material for both tools.", "answerCount": 7, "upvoteCount": 12, "datePublished": "2026-10-04T12:16:36Z", "dateModified": "2026-10-04T12:17:43Z", "author": { "@type": "Person", "name": "Anonymous", "url": "https://www.ok-tool.com/qa/p20-vs-s136-steel-high-volume-injection-molds.html" } ,"acceptedAnswer": { "@type": "Answer", "text": "First, map your two separate tool requirements directly to the inherent material properties of P20 and S136 to avoid blanket decisions. P20 is a pre-hardened low-alloy mold steel with a typical hardness range of 28-32 HRC, while S136 is a martensitic stainless steel that reaches 48-52 HRC after full quenching. The 42% upfront cost gap your procurement team identified in 2026 pricing is driven by S136’s higher raw material purity, additional heat treatment steps, and corrosion resistance alloy content, not arbitrary markup. For the black ABS structural housing mold that targets 80,000 annual cycles, P20 is fully sufficient as long as you implement two small control measures. ABS with no corrosive flame retardant additives will not accelerate P20 rust formation, and 80k cycles sit well below P20’s standard fatigue life limit of 150,000 runs for non-abrasive, non-corrosive resins. You can skip full S136 specification for this tool to lock in the 42% cost savings, and allocate the leftover budget to secondary polish upgrades if you need a finer surface finish than standard P20 as-milled texture. For the clear medical-grade PP enclosure mold, S136 is non-negotiable here. The trace slip agents and peroxide residues in medical PP will cause P20 surface micro-corrosion after 60,000-80,000 runs, which will leave hazy spots on your clear parts that no in-mold cleaning can fully remove. You can opt for pre-hardened S136 HRC 32 instead of full quenched S136 to cut 18% of the mold cost while retaining 90% of the corrosion resistance you need for the 300k cycle target, which balances budget constraints and performance requirements. To avoid common mistakes that many NPI teams make with this material pair, do not apply S136 for low-cycle non-cosmetic molds as a one-size-fits-all upgrade, as the extra cost will never be recovered in your total part cost per unit. Allocate 2 hours of extra IQC inspection for incoming P20 mold steel blanks to confirm hardness values fall within 28-32 HRC with no soft spots , which eliminates the risk of unexpected tool wear mid-run. For S136 blanks, verify that the supplier has done stress relief treatment before CNC machining to reduce post-processing deformation risk. After trial run sign-off, implement a simple mold maintenance log that requires a thin layer of anti-rust spray to be applied immediately after every production stop longer than 72 hours for the P20 tool. This simple step extends P20’s actual service life by more than 40% for non-corrosive resin runs , closing most of the performance gap with S136 for low to medium volume applications.", "upvoteCount": 12, "url": "https://www.ok-tool.com/qa/p20-vs-s136-steel-high-volume-injection-molds.html#acceptedAnswer", "datePublished": "2026-10-04T14:03:58Z", "author": {"@type": "Person","name": "David Zhang","url": "https://www.ok-tool.com/team/david.html"} } ,"suggestedAnswer": [ { "@type": "Answer", "text": "The hardness consistency of as-received P20 and S136 blanks will directly impact your total part cost per unit over the full product lifecycle. For the non-critical black ABS housing, even if P20 only lasts 120k cycles instead of 150k, the extra cost of a single mold repair at 100k cycles is still 60% lower than the upfront premium for S136. For medical grade PP applications, S136’s stain resistance means you will not need to stop production every 200 cycles to wipe down the mold surface to remove residue buildup, which cuts your unplanned downtime rate by more than 70% during mass production. You can also consider P20 with a surface nitriding treatment for mid-tier applications that need slightly better wear resistance without switching to full S136, but note that nitrided P20 still does not match S136’s corrosion resistance for acidic or additive-rich resins.", "upvoteCount": 0, "url": "https://www.ok-tool.com/qa/p20-vs-s136-steel-high-volume-injection-molds.html#suggestedAnswer-2", "datePublished": "2026-10-04T13:28:33Z", "author": {"@type": "Person","name": "Sophia Wang","url": "https://www.ok-tool.com/team/sophia.html"} } , { "@type": "Answer", "text": "The two steels have different thermal conductivity values that will change your injection cycle time significantly. P20 has a thermal conductivity of roughly 29 W/mK, while S136 at full hardened state sits around 18 W/mK. For the 80k run ABS housing, using P20 will reduce your cooling time by 12-15% per shot, which adds up to over 100 hours of total saved production time across the full production run. If you force S136 for this non-critical part, you will need to adjust cooling line layout to compensate for slower heat dissipation, otherwise you will face higher part warpage and longer cycle times that eat into your production capacity. For the clear PP parts, the lower thermal conductivity of S136 is not a downside, as it enables more uniform cooling across the full cavity surface, which reduces flow mark and haze defect rates for transparent components.", "upvoteCount": 0, "url": "https://www.ok-tool.com/qa/p20-vs-s136-steel-high-volume-injection-molds.html#suggestedAnswer-3", "datePublished": "2026-10-04T13:12:51Z", "author": {"@type": "Person","name": "Daniel Yang","url": "https://www.ok-tool.com/team/daniel.html"} } , { "@type": "Answer", "text": "Your incoming inspection criteria for these two mold steels can be adjusted to match your actual usage requirements to avoid unnecessary quality overchecks that delay trial preparation. For P20 blanks, only test three key parameters: surface decarburization layer depth, hardness uniformity across the full block, and sulfur content below 0.01% to prevent micro-cracking during long cycle runs. For S136 blanks, add a copper sulfate spot test to verify full corrosion resistance performance, to avoid situations where suppliers pass off ordinary 420 stainless steel as premium S136 to cut costs. After the mold is completed, the first 50 sample parts from P20 and S136 molds can be batch tested for surface roughness consistency, and you will find that S136 maintains 98% of its initial polish finish after 1000 cycles, while P20’s surface roughness will degrade by around 12% after the same run count.", "upvoteCount": 0, "url": "https://www.ok-tool.com/qa/p20-vs-s136-steel-high-volume-injection-molds.html#suggestedAnswer-4", "datePublished": "2026-10-04T12:59:52Z", "author": {"@type": "Person","name": "Jason Zhou","url": "https://www.ok-tool.com/team/jason.html"} } , { "@type": "Answer", "text": "The machining time for P20 and S136 mold cavities varies by a noticeable margin that many teams do not account for in their total tooling budget. Pre-hardened P20 cuts much faster on standard CNC mills, with tool life for regular carbide end mills reaching 12-15 hours per set, while machining full hardened S136 reduces end mill life by 50% or more. For the mirror polish you need on the clear PP cavity, S136 can be polished to A2 or A1 grade much more easily without generating micro-scratches, while P20 will need 30% more manual polishing hours to reach the same finish level, and still tends to retain tiny pinhole marks from non-metallic inclusions in the steel structure. If you choose pre-hardened S136 at 32 HRC instead of full quenched S136, your CNC machining time will be almost identical to machining P20, which eliminates most of the hidden machining cost premium for S136.", "upvoteCount": 0, "url": "https://www.ok-tool.com/qa/p20-vs-s136-steel-high-volume-injection-molds.html#suggestedAnswer-5", "datePublished": "2026-10-04T12:54:56Z", "author": {"@type": "Person","name": "Olivia Chen","url": "https://www.ok-tool.com/team/olivia.html"} } , { "@type": "Answer", "text": "There are small design adjustments you can make to your part geometry to accommodate each steel’s inherent properties and reduce tooling risk. For the P20 mold for the black ABS housing, you can reduce the minimum draft angle for side walls by 0.5 degrees, since P20’s lower hardness means it has lower friction against the flowing resin during ejection. For S136 molds, avoid sharp internal corners that have a radius smaller than 0.8mm, as full hardened S136 has higher notch sensitivity and is more prone to micro-chipping at sharp edges under repeated high injection pressure. If you have any small raised text or fine texture features on the part surface, S136 can hold these features clearly for 300k+ cycles with no edge blurring, while P20’s edges will start to wear after 120k cycles, requiring you to re-engrave the text twice over the full product lifecycle.", "upvoteCount": 0, "url": "https://www.ok-tool.com/qa/p20-vs-s136-steel-high-volume-injection-molds.html#suggestedAnswer-6", "datePublished": "2026-10-04T12:19:17Z", "author": {"@type": "Person","name": "Kevin Liu","url": "https://www.ok-tool.com/team/kevin.html"} } , { "@type": "Answer", "text": "You can split the mold manufacturing timeline to accommodate the different lead times of P20 and S136 to hit your 6-week trial run target. P20 blanks are almost always in stock at local steel suppliers, so you can receive the raw material in 2-3 working days, while standard S136 blanks require 7-10 days of lead time if you need full quenched and stress relieved material. This means you can start rough machining the P20 ABS housing mold 1 week earlier to catch up on any unplanned delays during tooling, while scheduling the S136 clear PP mold to enter the production queue right after raw material arrival. If your project timeline slips by 3 days for any reason, you can also use pre-hardened P20 to produce a temporary spare mold for the black ABS parts, which can be finished in half the time of a S136 spare, to ensure you do not miss your mass production launch window even if you encounter unexpected tool damage during trial runs.", "upvoteCount": 0, "url": "https://www.ok-tool.com/qa/p20-vs-s136-steel-high-volume-injection-molds.html#suggestedAnswer-7", "datePublished": "2026-10-04T12:17:43Z", "author": {"@type": "Person","name": "Eric Zhao","url": "https://www.ok-tool.com/team/eric.html"} } ] } }, { "@context": "https://schema.org", "@type": "BreadcrumbList", "itemListElement": [ {"@type": "ListItem", "position": 1, "name": "Home", "item": "https://www.ok-tool.com/"},{"@type": "ListItem", "position": 2, "name": "Q&A", "item": "https://www.ok-tool.com/qa/"},{"@type": "ListItem", "position": 3, "name": "Injection Molding Q&A", "item": "https://www.ok-tool.com/qa/injection-molding/"} ,{"@type": "ListItem", "position": 4, "name": "P20 vs S136 steel: which is better for high volume plastic injection molds?"} ] } ] ```