Description of raw materials for hydraulic fittings - carbon steel

Carbon steel is an iron carbon alloy with carbon content ranging from 0.0218% to 2.11%. Also called carbon steel. Generally also contains a small amount of silicon, manganese, sulfur, phosphorus. The higher the carbon content in the general carbon steel, the greater the hardness, the higher the strength, but the lower the plasticity.

About heat treatment of carbon steel,we need to know the following information.

I. Purpose of the experiment

1) Understand the basic heat treatment process of carbon steel 

2) Study the relationship between cooling conditions and steel properties

3) Analyze the influence of quenching and tempering temperature on steel properties

2. Experimental equipment and specimens

1)Experimental equipment :SX-10M-2.5 type box test resistance furnace

2)Specimen :45 steel, 30 steel and T8 steel specimen

3) Three specimens of 45 steel after quenching

3. the experimental principle

Heat treatment is an important metalworking process to improve the performance of steel (service performance and process performance). The process of heat treatment of steel is characterized by heating the steel to a certain temperature, holding it for a certain time, and then cooling it at a certain cooling rate. The properties of steel are changed through this process.

4. Experiment content and procedure

(1) Quenching heat treatment of steel

Quenching heat treatment is to heat carbon steel to AC3 or AC1 above 30-50°C, after insulation into different cooling medium for rapid cooling (cooling speed is greater than the critical cooling speed), in order to get martensitic structure (M). After quenching, the microstructure is martensite and retained austenite.

1. Determination of quenching temperature

Depending on the material, find its critical temperature AC3 or AC1 in Table 1 and add 40°C to get its heating temperature.

Hypoeutectoid steel (45, 30):

Heating temperature =AC3 + 40°C

Eutectoid steel (T10 steel): 

Heating temperature =AC1 + 40°C

So the final heating temperature of 30 steel = °C + 40°C=

45 steel heating temperature = °C + 40°C=

45 steel heating temperature = °C + 40°C=

2. Determination of insulation time

Parts with the furnace heating to reach the required heating temperature, but also for a period of heat preservation, to ensure that the whole parts evenly and fully reach the required temperature. Obviously, the holding time is related to the size and shape of the work piece.

By measuring the dimensions of the parts, then refer to Table 2 to calculate the holding time of the specimen.

The dimensions of the parts are cylindrical parts with a diameter of 20 mm, so the holding time of steel 30, 45 and T10 is: 

3. Selection of cooling medium

Cooling is the key process of quenching. It directly affects the properties of hardened steel. Quenching cooling rate is greater than the critical cooling rate to obtain super-cooled martensite structure. At the same time, the internal stress in the crystallization process should be controlled in the cooling process to prevent deformation and cracking.

In order to ensure the quenching effect, appropriate cooling medium and cooling method should be selected. In this experiment, we chose water at room temperature as the cooling medium.

4. Put the work-piece into the furnace, set the heating control temperature of the electric furnace temperature controller, and start heating.

5. After the furnace reaches the set temperature, start the time of insulation.

6. The work-piece is out of the oven and quickly put into the water for cooling.