Chapter 7Chapter 7Chapter 7Chapter 7

§7.2§7.2 The Basic Knowledge The Basic Knowledge

Smelt process of steels and effects on the Smelt process of steels and effects on the quality of them quality of them smelt principlessmelt principles effects of furnace and deoxygenate degreeeffects of furnace and deoxygenate degree

ClassificationClassification by chemical componentby chemical component by qualityby quality by structure usesby structure uses

Put the fusedPut the fused molten iron molten iron or or cokecoke and and iron oreiron ore to the oven for fining to make to the oven for fining to make charchar and other and other impuritiesimpurities volatilization volatilization through oxidation or change them into through oxidation or change them into oxide to become slag. All these can oxide to become slag. All these can reduce the impurity.reduce the impurity.

Smelt principlesSmelt principles

Smelt process of steels and effects on Smelt process of steels and effects on the quality of themthe quality of them

ProcessProcess

cokecoke

ironstone

ironstonepig iron

pig iron

blast furnace

melt

pig ironpig iron

smelt

oxidizeoxidizedeoxidizedeoxidize

steelsteel

CastCast ingotingot

steel ingotsteel ingotconstruction construction

steelsteel

Fig.7.2.1 Smelt process of steelFig.7.2.1 Smelt process of steel

Effects of furnace and Effects of furnace and deoxygenate degreedeoxygenate degree

Effect of furnace and deoxidation degree are listed in Tab.7.2.1 and Tab.7.2.2

Tab.7.2.1 Effect of FurnaceEffect of FurnaceFurnace Furnace modelmodel

MaterialMaterialInbreatInbreathe gashe gas

Smelt Smelt timetime

Steel Steel qualityquality

CostCost UsesUses

Oxygen Oxygen converterconverter

Melt Melt molten molten

ironiron

Pure Pure oxygenoxygen

15-15-30min 30min

HighHigh LowLow

High High quality quality

carbon steel carbon steel and alloy and alloy

steelsteel

Even Even furnacefurnace

Pig iron, Pig iron, ironstoneironstone

AirAir 5-12hr 5-12hr HighHigh HighHigh

The same The same above and above and

especial especial steelsteel

Electric Electric cookercooker

Steel Steel waste,pig waste,pig

ironironAirAir short short

ExcelleExcellentnt

HighHighThe same The same

aboveabove

The process of deoxidation will get rid of the impuritiesSome of the iron will inevitably be oxidized advances the occurrence of large quantiti

es of air bubbles affects the quality of the steel

In order to deoxidize FeO and Fe2O3 into iron, we must add deoxidant in the later period.

Deoxidation degreeDeoxidation degree

Tab.7.2.2 Deoxidation degree and steels quality

Types of Types of steelsteel

Deoxidation Deoxidation degreedegree

Cooling circsCooling circs Steels qualitySteels quality

Boiling steelBoiling steel Low Low Large amounts of Large amounts of CO floating while CO floating while

pouring pouring UnqualifiedUnqualified

Half Half sedation sedation

steelsteelMedium Medium ExcellentExcellent

Sedation Sedation steelsteel

HighHighNo CO floating in No CO floating in

the air while the air while cooled still cooled still

Dense tissue ,well-Dense tissue ,well-distribution,excelledistribution,excelle

nt mechanical nt mechanical propertyproperty

Special Special sedation sedation

steelsteelThoroughThorough PerfectPerfect

1.1. Carbon SteelCarbon SteelLow Carbon Steel C<0.25% Low Carbon Steel C<0.25% √√

Medium Carbon Steel C=0.3Medium Carbon Steel C=0.3 ～～ 0.55% 0.55%

High Carbon Steel C>0.6% High Carbon Steel C>0.6%

2.2. Alloy steelAlloy steelLow Alloy Steel <5% Low Alloy Steel <5% √√

Medium Alloy Steel = 5Medium Alloy Steel = 5 ～～ 10% 10%

High Alloy Steel >10% High Alloy Steel >10%

by chemical Component

Tab.7.2.3 Chemical component of carbon steel （ GB700—88 ）

codecodenamenamess

gragra d dee

chemical component %chemical component %

oxigenate oxigenate methodmethod

C C Mn Mn

Si Si S S P P

≤≤

Q195 Q195 0.06~0.12 0.06~0.12 0.30 0.30 0.050 0.050 0.045 0.045 FF 、、 bb 、、 Z Z

Q215 Q215 AA

0.09~0.15 0.09~0.15 0.25~0.55 0.25~0.55 0.30 0.30 0.050 0.050

0.045 0.045 0.045 0.045 FF 、、 bb 、、 Z Z

BB

Q235 Q235

AA 0.14~0.220.14~0.22 0.30~0.650.30~0.65

0.30 0.30

0.0500.0500.045 0.045 FF 、、 bb 、、 Z Z

BB 0.12~0.200.12~0.20 0.30~0.700.30~0.70 0.0450.045

CC ≤≤0.180.18 0.35-0.80 0.35-0.80 0.040 0.040 0.040 0.040 Z Z

D D ≤≤0.17 0.17 0.035 0.035 0.035 0.035 TZ TZ

Q255 Q255 AA

0.18~0.28 0.18~0.28 0.40~0.70 0.40~0.70 0.30 0.30 0.050 0.050

0.045 0.045 Z Z BB 0.045 0.045

Q275 Q275 0.20~0.38 0.20~0.38 0.50~0.80 0.50~0.80 0.35 0.35 0.050 0.050 0.045 0.045 Z Z

by quality

Common Steel P≯0.045%,S≯0.055%

High Quality Steel

P≯0.035-0.04%,S≯0.04%

Advanced High Quality Steel P≯0.025%,S≯0.025%

by structure use

Structure Steel

Low-carbon steel, medium-carbon steel, kinds of engineering components and mechanical parts

Tool Steel

tools, mould

Special steel

stainless steel, heat-resistant steel, wear-resistant steel