Stainless Steel Essay

Summary

This report looks at how heat tempering, solution annealing and cold work hardening, can change the properties of stainless steel. There are three main grades of stainless steel, these grades are ferritic, Austenitic and Martensitic. These grades have different ways of hardening. There are other grades of Stainless Steels that don’t fit in with the other grades, these are known as special stainless steels and are prescription hardenable.

Introduction

Stainless steels are used in every day applications such as oil and gas, medical equipment, cutlery, boats and many more. The discovery of stainless steel is not very well known, as Germany, Britain, Poland, France, America and Sweden have all claimed that they discovered Stainless

He used steel alloys which had chromium in them. He then started experimenting with steel that used different chromium values between 6% and ranging all the way up to 15%, with varying amounts of carbon. During these experiments he created a steel that contained 0.24% carbon and 12.8% chromium. He argued that this was the first ever stainless steel.

Categories of stainless steel Stainless steel is normally classed as stainless steel if it contains 10% and above chromium. There are some steels that only contain 8% chromium and are classed as stainless steels. Stainless steel is used for its properties such as, erosion resistance and corrosion resistance. Some stainless steels such as type 422, have impact toughness and strength, with temperatures below 650 degrees

Compared to alloy steels, stainless steel is harder to forge. This is due to it needing a higher pressure to create a forged component, even though its done at the same temperature as steel alloys. There are three groups of stainless steel that are mainly looked at when forging, austenitic, ferritic and martensitic. These aren’t the only groups of stainless steels, there are many special types that do not come under these categories. There is a group of steel alloys that are in the forging category but considered special stainless steel, due to the heat resistant

these are stainless steel that a prescription hardenable (PH) such as 15-5PH, PH-13-8Mo and 17-4PH these alloys are used for forging. The alloys include Cr-Ni in their make-up, like austenitic materials. They have added metals such as aluminium, copper, titanium and columbium when other properties are required. These allow the stainless steels to be solution treated and age cycled, giving the material more strength. These materials, when in the annealed condition, are “soft martensitic” and are then made into “hard martensitic” by sub-zero cooling or age cycling. This gives the material properties of corrosion resistance and very good tensile and yield strengths. There is a grade of stainless steel called duplex. Duplex is almost twice as strong as 304- type stainless. This kind of stainless steel is normally used in nuclear components. Duplex has a higher chromium than prescription hardening types of stainless steel, it also contains less carbon but has similar nickel to PH grades of stainless steel. Other materials can be added to change the properties of