Stainless steel is an alloy of iron with small amounts of carbon and which major alloying element that primarily gives it corrosion resistance (stainless property)?

Introduction / Context:
This question concerns alloys and materials science. Stainless steel is widely used in kitchenware, construction, medical instruments and many other applications. The question asks which major alloying element, added to iron and carbon, gives stainless steel its characteristic corrosion resistant or stainless property.

Given Data / Assumptions:

• Stainless steel is based on iron, with small amounts of carbon.
• We are asked to identify the key added element responsible for corrosion resistance.
• Options include manganese, vanadium, chromium and other metals.
• We assume common grades of stainless steel used in industry.

Concept / Approach:
Stainless steel is defined as steel containing a significant proportion of chromium, usually at least about 10.5 percent by mass. Chromium forms a very thin, adherent oxide film on the surface that protects the underlying metal from further rusting. This phenomenon is called passivation. Without chromium, ordinary carbon steel rusts readily in moist air. Other elements like nickel, molybdenum or manganese may be added to tailor properties, but chromium is the essential alloying element that gives the stainless character.

Step-by-Step Solution:
1) Recognise that stainless steel is a special type of steel designed to resist corrosion.2) In standard definitions, stainless steels contain iron, carbon and a significant percentage of chromium.3) Chromium in the alloy reacts with oxygen at the surface to form a very thin, invisible chromium oxide layer.4) This oxide layer is stable, tightly adherent and self healing if scratched, preventing further penetration of oxygen and moisture.5) Manganese and vanadium can also be present in some steel grades but do not by themselves provide the main stainless property.6) Therefore, the major alloying element responsible for corrosion resistance in stainless steel is chromium.

Verification / Alternative check:
Metallurgical descriptions state that a steel must contain at least a certain minimum percentage of chromium to be called stainless. Common grades such as 304 stainless steel contain around 18 percent chromium and 8 percent nickel, while 430 stainless steel contains about 16 to 18 percent chromium without nickel. The presence of chromium is the common feature in these grades, confirming its central role. In contrast, steels without chromium but with other alloying elements do not show the same high level of corrosion resistance.

Why Other Options Are Wrong:
Manganese: It is used to improve strength and hardenability in some steels, but it is not the primary cause of stainless behaviour.
Vanadium: Often added to steel to increase strength and resistance to wear, but does not by itself create stainless steel.
Tin: Used in some alloys and coatings, but not the defining element of stainless steel.
Lead: Sometimes added in small amounts to free cutting steels to improve machinability, but not used to make stainless steels.

Common Pitfalls:
Students sometimes choose nickel because many stainless steels are described as chromium nickel alloys. While nickel improves toughness and resistance to certain types of corrosion, chromium is still the essential element that defines stainless steel. If you remember that the term stainless is closely associated with chromium oxide passivation, it becomes easier to identify chromium as the correct answer whenever the key corrosion resisting element in stainless steel is asked.

Final Answer:
Stainless steel contains iron and carbon along with chromium as the major alloying element that provides corrosion resistance.