Stainless Steel Composition for Hardness and Acid Resistance
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Solution Overview
Problem
Existing stainless steel technologies face challenges in simultaneously achieving high surface hardness, internal hardness, and corrosion resistance, particularly in non-oxidative acids, while maintaining good cold workability.
Innovation Solution
A stainless steel composition with specific element ratios (0.18% to 0.25% C, 0.1% to 1.5% Si, 0.35% to 1.5% Mn, 0.04% or less P, 0.01% or less S, 0.05% to 0.20% Ni, 12.5% to 14.6% Cr, 1.5% to 3.0% Mo and/or W, 1.0% to 3.0% Cu, 0.03% to 0.10% N, and Fe with a coarse Cu phase area ratio of 2.4% or more) is combined with a manufacturing process involving controlled annealing at 760°C to 780°C, quenching in a nitrogen atmosphere, sub-zero treatment, and tempering at 150°C to 470°C to enhance hardness and corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional quenching and tempering is used to increase surface hardness, then surface hardness is improved, but corrosion resistance deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the carbon content within 0.18% to 0.25% and copper content within 1.0% to 3.0%, along with specific annealing temperature ranges, to achieve a balance where the steel attains sufficient surface hardness through controlled martensitic transformation while maintaining corrosion resistance through optimized compositional parameters that prevent excessive carbide precipitation
2Reliability
If annealing temperature is increased to 788°C to 843°C, then corrosion resistance is improved, but cold workability deteriorates due to precipitation hardening
Solution Approach 1:
The patent resolves this contradiction by changing the annealing temperature parameter to a lower range of 760°C to 780°C, which is sufficient to achieve the desired corrosion resistance through controlled microstructure development while avoiding the precipitation hardening that would occur at higher temperatures, thereby preserving cold workability
Solution Approach 2:
The patent applies local quality by creating a specific microstructural configuration where copper phases are distributed in a controlled manner within the martensitic matrix, achieving localized properties that provide both corrosion resistance and maintain ductility for cold working
3Strength
If copper content is increased to 1.5% to 4.0%, then surface hardness is improved, but cold workability deteriorates due to precipitation hardening
Solution Approach 1:
The patent applies parameter changes by optimizing the copper content within the specific range of 1.0% to 3.0%, which provides sufficient copper-induced hardening and corrosion resistance while avoiding excessive precipitation that would compromise cold workability. This precise parameter control allows the steel to achieve the desired balance of properties
4Strength
If internal hardness is increased to improve product strength, then product internal strength is improved, but corrosion resistance may deteriorate
Solution Approach 1:
The patent resolves this contradiction by controlling the carbon content within 0.18% to 0.25% and applying specific heat treatment parameters, which achieve sufficient internal hardness (480 HV or more) through controlled martensitic transformation while maintaining corrosion resistance by avoiding excessive carbide precipitation that would deplete chromium from the matrix
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution results in a stainless steel product with surface hardness of 630 HV or more, internal hardness of 480 HV or more, and excellent corrosion resistance against non-oxidative acids, while maintaining good cold workability.
Implementation Method 1
performing annealing at 760°C to 780°C for four hours or more
Implementation Method 2
quenching in a nitrogen atmosphere
Implementation Method 3
sub-zero treatment
Implementation Method 4
tempering at 150°C to 470°C
Implementation Method 5
a solid-phase nitrogen absorption process in which nitrogen is dissolved on the surface at a high temperature of approximately 1000°C
Implementation Method 6
a nitriding process of forming a nitride layer on the surface
Data Source
Figure 1~3
AI summary
Provided are a stainless steel having excellent cold workability and a manufacturing method therefor; and a stainless steel product for which surface hardness is sufficiently high and for which corrosion resistance against acids, particularly non-oxidative acids, is excellent and a manufacturing method therefor. Provided are the stainless steel and the manufacturing method therefor, said steel having a component composition, in terms of % by mass, 0.18-0.25% of C, 0.1-1.5% of Si, 0.35-1.5% of Mn, 0.04% or less of P, 0.01% or less of S, 0.05-0.20% of Ni, 12.5-14.6% of Cr, 1.5-3.0% of one or both of Mo and W according to the relational expression (Mo + 1/2W), 1.0-3.0% of Cu, and 0.03-0.10% of N, the remainder being Fe and impurities. Further provided are the stainless steel product and the manufacturing method therefor, said stainless steel product being obtained by quenching and tempering the foregoing stainless steel.